Noticed this when I was rolling out 1.31.0-wmf.24. Not very noisy, but spikes occasionally.
#0 /srv/mediawiki/php-1.31.0-wmf.24/includes/specials/pagers/BlockListPager.php(171): MWExceptionHandler::handleError(integer, string, string, integer, array, array)
#1 /srv/mediawiki/php-1.31.0-wmf.24/includes/pager/TablePager.php(192): BlockListPager->formatValue(string, NULL)
#2 /srv/mediawiki/php-1.31.0-wmf.24/includes/pager/IndexPager.php(445): TablePager->formatRow(stdClass)
#3 /srv/mediawiki/php-1.31.0-wmf.24/includes/pager/TablePager.php(101): IndexPager->getBody()
#4 /srv/mediawiki/php-1.31.0-wmf.24/includes/specials/SpecialBlockList.php(195): TablePager->getFullOutput()
#5 /srv/mediawiki/php-1.31.0-wmf.24/includes/specials/SpecialBlockList.php(115): SpecialBlockList->showList(BlockListPager)
#6 /srv/mediawiki/php-1.31.0-wmf.24/includes/specialpage/SpecialPage.php(522): SpecialBlockList->execute(NULL)
#7 /srv/mediawiki/php-1.31.0-wmf.24/includes/specialpage/SpecialPageFactory.php(579): SpecialPage->run(NULL)
#8 /srv/mediawiki/php-1.31.0-wmf.24/includes/MediaWiki.php(288): SpecialPageFactory::executePath(Title, RequestContext)
#9 /srv/mediawiki/php-1.31.0-wmf.24/includes/MediaWiki.php(861): MediaWiki->performRequest()
#10 /srv/mediawiki/php-1.31.0-wmf.24/includes/MediaWiki.php(524): MediaWiki->main()
#11 /srv/mediawiki/php-1.31.0-wmf.24/index.php(42): MediaWiki->run()
#12 /srv/mediawiki/w/index.php(3): include(string)
#13 {main}